The present invention is related to a pulse width modulation integrated circuit (IC) chip, and more particularly to a pulse width modulation integrated circuit chip available as an 8-pin DIP (dual-in-line package) or a 14-pin SOP (small-outline package) package.
In the technical field associated with switching mode power supply (SMPS), the pulse width modulation integrated circuit (PWM IC) is applied to drive a switching transistor to switch its on/off states, so as to generate an input DC voltage by rectifying and filtering the input AC voltage of the commercially available power source. The transformer of a switching mode power supply is coupled in series with a switching transistor to convert the input DC voltage into AC voltage, thereby conveying the energy of the transformer to its secondary side and providing an output DC voltage for a load by performing rectification/filtering operations.
It can be understood by way of the above statements that the PWM IC is employed as the major control circuit in a switching mode power supply and a common voltage regulator. However, in order to allow the PWM IC to be more adapted for use in a switching mode power supply and heighten its performance, there is a need to develop a PWM IC with simpler circuit layout, less pin number, higher package density and lower cost.
It is highly desirable to address a novel circuit layout for a PWM IC with high package density and less pin number, which can provide complete voltage regulation function through the use of less pins, and is advantageous in terms of cost descent and power density promotion.
The foregoing objects can be fulfilled by a PWM IC chip presented as an 8-pin DIP (dual-in-line package) package or a 14-pin SOP (small outline package) package. The present invention provides a PWM IC chip including a plurality of internal control circuits, each of the internal control circuits respectively creates and defines a pin function. These internal control circuits can be used to sense the external linear voltage and compare the sensed external voltage with the internal reference voltage, and output a control signal in response to the comparison result to switch the states of a switch of the internal power control circuit in the PWM IC. In addition, the present invention uses an internal current source to implement the control function of these internal control circuits, for example, modulate the operation frequency of the PWM IC, accomplish the voltage feedback operation for the power supply, sense the external current value and control the PWM IC to increase the pulse width of the output pulse signal tardily when undergoing an power initialization. As a result, most of the pin functions of the PWM IC of the present invention is created and defined by internal current sources instead of external voltage sources, so that the complexity of circuit layout is greatly simplified.
Now the foregoing and other features and advantages of the present invention will be more clearly understood through the following descriptions with reference to the accompanying drawings, wherein: